int main()
{
    int arr[] = { 1,2,2,3,3,4,1 };
    int dog = 0;
    int sz = sizeof(arr) / sizeof(arr[0]);
    for (int i = 0; i < sz; i++)
    {
        dog ^= arr[i];
    }
    printf("单身狗 是%d", dog);
    return 0;
}


